Initiation of translation usually involves the interaction of certain key proteins with a special tag bound to the 5′-end of an mRNA molecule, the 5′ cap. Protein factors bind the small ribosomal subunit (also referred to as the 40 S subunit), and these “initiation factors” hold the mRNA in place. The eukaryotic Initiation Factor 3 (eIF3) is associated with the small ribosomal subunit, and plays a role in keeping the large ribosomal subunit from prematurely binding. eIF3 also interacts with the eIF4F complex which consists of three other initiation factors: eIF4A, eIF4E and eIF4G. eIF4G is a scaffolding protein that directly associates with both eIF3 and the other two components. eIF4E is the cap-binding protein. It is the rate-limiting step of CAP-dependent initiation, and is often cleaved from the complex by viral proteases to limit the cell's ability to translate its own transcripts. This is a method of hijacking the host machinery in favor of the viral (cap-independent) messages.